Rubber composition for hose and hose

ABSTRACT

A rubber composition for a hose, which comprises a nitrile rubber (A) comprising 45-55 weight % of α,β-ethylenically unsaturated nitrile monomer units and 55-45% by weight of conjugated diene monomer units, an epihalohydrin rubber (B), and a crosslinking agent (C A ) for the nitrile rubber and/or a crosslinking agent (C B ) for the epihalohydrin rubber; the amount of nitrile rubber (A) being 25-80 weight % based on the sum of nitrile rubber (A) and epihalohydrin rubber (B); and a hose having a layer comprised of a crosslinked product of the rubber composition. The hose has excellent resistance to fuel oil permeation and cold resistance, and therefore, it is especially suitable as fuel oil hoses of an automobile.

TECHNICAL FIELD

This invention relates to a rubber composition comprising a nitrilerubber and an epihalohydrin rubber. More particularly it relates to arubber composition for hoses comprising a specific nitrile rubber,epihalohydrin rubber and a specific crosslinking agent, which hasenhanced resistance to fuel oil permeation and cold resistance. Thisinvention further relates to a hose having a layer comprised of acrosslinked product of the rubber composition for hoses.

BACKGROUND ART

For fuel hoses of automobiles, enhanced resistance to fuel oilpermeation and cold resistance are required for controlling dissipationof fuel oil such as gasoline into the air and preventing embrittlementunder severe cold conditions, for example, at a temperature of −30° C.As rubber materials for fuel hoses, nitrile rubber, a polyblend ofnitrile rubber and vinyl chloride resin (PVC) and epihalohydrin rubberare widely used.

In recent years, regulations for controlling automobile exhaust havebecome tightened to preserve the environment. Thus, hoses having goodresistance to fuel oil permeation are desired. As techniques forenhancing the resistance to fuel oil permeation, there can be mentionedan attempt of increasing the wall thickness of hoses and an attempt ofusing a rubber material having excellent resistance to fuel oilpermeation. However, the increase of the wall thickness of hosescontradictory to requirement of weight-saving of automobiles. Recenttendency of miniaturization and high integration of automobile enginesmakes it difficult to install hoses with a thick wall within a limitedspace. Therefore a rubber material exhibiting excellent resistance tofuel oil permeation is eagerly desired.

To comply with the above-requirement, in the case of nitrile rubberhoses, an attempt of increasing the content of α,β-ethylenicallyunsaturated nitrile monomer units in the nitrile rubber is considered.This attempt enhances the resistance to fuel oil permeation, but reducesthe cold resistance. Thus the hoses cannot be used in cold districts.

In the case of hoses of the nitrile rubber/vinyl chloride resin, anattempt of increasing the content of α,β-ethylenically unsaturatednitrile monomer units in the nitrile rubber and an attempt of increasingthe proportion of PVC resin in the polyblend are considered. Theseattempts contribute to enhancement of the resistance to fuel oilpermeation, but the cold resistance is reduced. Further PVC is notdesired from the viewpoint of environment preservation.

In the case of hoses of epihalohydrin rubber, the resistance to fuel oilpermeation increases with an increase of the content of epihalohydrinunits in the rubber, but, the resistance to fuel oil permeation issometimes not to the desired even though the rubber is an epihalohydrinhomopolymer. That is, an improvement of resistance to fuel oilpermeation to the satisfying extent has been difficult. Further, theincrease of the epihalohydrin unit content in the rubber leads toreduction of the cold resistance.

DISCLOSURE OF THE INVENTION

In view of the foregoing, an object of the present invention is toprovide a hose having improved resistance to fuel permeation and coldresistance, and further to provide a rubber material used for theproduction thereof.

The present inventors made extensive researches to achieve theabove-mentioned object, and have found that a rubber compositioncomprising a specific nitrile rubber (A), epihalohydrin rubber (B) and aspecific crosslinking agent, wherein the ratio in amount of nitrilerubber (A)/epihalohydrin rubber (B) is in a specific range, exhibitsenhanced resistance to fuel consumption and cold resistance. Based onthis finding, the present invention has been completed.

Thus, in accordance with the present invention, there is provided arubber composition for a hose, which comprises a nitrile rubber (A)comprising 45 to 55% by weight of α,β-ethylenically unsaturated nitrilemonomer units and 55 to 45% by weight of conjugated diene monomer units,an epihalohydrin rubber (B), and a crosslinking agent (C_(A)) for thenitrile rubber (A) and/or a crosslinking agent (C_(B)) for theepihalohydrin rubber (B); the amount of the nitrile rubber (A) being inthe range of 25 to 80% by weight based on the sum of the nitrile rubber(A) and the epihalohydrin rubber (B); and further provided a hose havinga layer comprised of a crosslinked product of the rubber composition.

BEST MODE FOR CARRYING OUT THE INVENTION

Rubber Composition

The rubber composition for a hose, of the present invention comprises anitrile rubber (A) comprising 45 to 55% by weight of α,β-ethylenicallyunsaturated nitrile monomer units and 55 to 45% by weight of conjugateddiene monomer units, an epihalohydrin rubber (B), and a crosslinkingagent (C_(A)) for the nitrile rubber (A) and/or a crosslinking agent(C_(B)) for the epihalohydrin rubber (B), wherein the amount of nitrilerubber (A) being in the range of 25 to 80% by weight based on the sum ofnitrile rubber (A) and epihalohydrin rubber (B).

Nitrile Rubber (A)

The nitrile rubber (A) used in the present invention containsα,β-ethylenically unsaturated nitrile monomer units and conjugated dienemonomer units.

The α,β-ethylenically unsaturated nitrile monomer is not particularlylimited, and includes, for example, acrylonitrile and methacrylonitrile.Of these, acrylonitrile is preferable in view of the good resistance tofuel oil.

The content of α,β-ethylenically unsaturated nitrile monomer units innitrile rubber (A) is such that the lower limit is 45% by weight,preferably 47% by weight, and the upper limit is 55% by weight,preferably 53% by weight. If the content of α,β-ethylenicallyunsaturated nitrile monomer units is too low, the resistance to fuel oilpermeation is reduced. In contrast, if the content thereof is too high,the cold resistance is reduced.

The conjugated diene monomer is also not particularly limited, andincludes, for example, 1,3-butadiene, 2-methyl-1,3-butadiene,1,3-pentadiene and 2-chloro-1,3-butadiene. Of these, 1,3-butadiene ispreferable in view of the good cold resistance.

The content of conjugated diene monomer units in nitrile rubber (A) issuch that the lower limit is 45% by weight, preferably 47% by weight,and the upper limit is 55% by weight, preferably 53% by weight. If thecontent of conjugated diene monomer units is too low, the coldresistance is reduced. In contrast, if the content thereof is too high,the resistance to fuel oil permeation is reduced.

The nitrile rubber used in the present invention may contain othercopolymerizable monomer units. The copolymerizable monomer includes, forexample, α-olefin monomers, α,β-ethylenically unsaturated carboxylicacid monomers, α,β-ethylenically unsaturated carboxylic acid estermonomers, α,β-ethylenically unsaturated carboxylic acid amide monomers,vinyl aromatic monomers, carboxylic acid ester monomers ofα,β-ethylenically unsaturated alcohols, α,β-ethylenically unsaturatedketone monomers and α,β-ethylenically unsaturated ether monomers.

As specific examples of the α-olefin monomer, there can be mentionedethylene, propylene and 1-butene.

As specific examples of the α,β-ethylenically unsaturated carboxylicacid monomer, there can be mentioned monocarboxylic acids such asacrylic acid and methacrylic acid; polycarboxylic acids such as maleicacid, fumaric acid and itaconic acid; and partial esters ofpolycarboxylic acids such an monobutyl fumarate ester, monobutyl maleateester and monoethyl itaconate ester.

As specific examples of the α,β-ethylenically unsaturated carboxylicacid ester monomer, there can be mentioned alkyl esters such as methylacrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate andlauryl methacrylate; alkoxy-substituted alkyl esters such asmethoxyethyl acrylate and methoxyethoxyethyl acrylate; cyano-substitutedalkyl esters such as cyanomethyl acrylate, 2-cyanoethyl acrylate,2-ethyl-6-cyanohexyl acrylate; hydroxy-substituted alkyl esters such as2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate;epoxy-substituted alkyl esters such as glycidyl acrylate and glycidylmethacrylate; amino-substituted alkyl esters such asN,N′-dimethylaminoethyl acrylate; halogen-substituted alkyl esters suchas 1,1,1-trifluoroethyl acrylate; and complete esters of polycarboxylicacids such as diethyl maleate, dibutyl fumarate and dibutyl itaconate.

As specific examples of the α,β-ethylenically unsaturated carboxylicacid amide monomer, there can be mentioned acrylamide, methacrylamide,N,N′-dimethylacrylamide, N-butoxymethylacrylamide,N-butoxymethylmethacrylamide, N-methylolacrylamide andN,N′-dimethylolacrylamide.

As specific examples of the vinyl aromatic monomer, there can bementioned styrene, α-methylstyrene, ethylstyrene, butylstyrene,phenylstyrene, vinylnaphthalene, vinylanthracene, butoxystyrene,phenoxystyrene, vinylbenzoic acid, vinylsalicyclic acid, aminostyrene,cyanostyrene, nitrostyrene, chlorostyrene and chloromethylstyrene.

As specific examples of the carboxylic acid ester monomer of anα,β-ethylenically unsaturated alcohol, there can be mentioned vinylacetate, isopropenyl acetate, vinyl benzoate and vinyl chloroacetate. Asspecific examples of the α,β-ethylenically unsaturated ketone monomer,there can be mentioned vinyl ethyl ketone and vinyl phenyl ketone. Asspecific examples of the α,β-ethylenically unsaturated ether monomer,there can be mentioned vinyl methyl ether, vinyl butyl ether, vinyl2-ethylhexyl ether, vinyl phenyl ether, vinyl glycidyl ether and allylglycidyl ether.

Further, the copolymerizable monomer includes vinyl chloride, vinylidenechloride and vinylpyridine.

The permissible upper limit of the amount of the copolymerizable monomerin nitrile rubber (A) is preferably 10% by weight, more preferably 6% byweight. When the amount of the copolymerizable monomer is too large, theresulting hose exhibits a reduced elongation and is liable to be crackedor broken, when it is used for a long period at a high temperature.

The Mooney viscosity (ML₁₊₄, 100° C.) of nitrile rubber (A) is notparticularly limited, but, its lower limit is preferably 25, morepreferably 35 and especially preferably 45, and its upper limit ispreferably 140, more preferably 120 and especially preferably 100. Whenthe Mooney viscosity is too high or too low, the processability ofrubber is degraded.

Epihalohydrin Rubber (B)

Epihalohydrin rubber (B) used in the present invention includes ahomopolymer comprising epihalohydrin monomer units, copolymerscomprising two or more kinds of epihalohydrin monomer units, andcopolymers comprising epihalohydrin monomer units and othercopolymerizable monomer units. Epihalohydrin rubber (B) is preferably anepihalohydrin copolymer containing unsaturated epoxide monomer units inview of the mechanical strength.

The epihalohydrin monomer is a compound prepared by substituting ahydrogen atom of ethylene oxide with a halomethyl group, and includes,for example, epihalohydrin, epibromohydrin and β-methylepichlorohydrin.The epihalohydrin monomers may be used as a combination of two or morethereof. Of these, epihalohydrin is preferable because of ease inavailability. The content of epihalohydrin monomer units inepihalohydrin rubber (B) is usually at least 40% by weight.

The copolymerizable monomer used for copolymerization includes, forexample, alkylene oxides and unsaturated epoxides.

As specific examples of the alkylene oxide, there can be mentionedethylene oxide, propylene oxide, 1,2-epoxybutane, 1,2-epoxyisobutane,2,3-epoxybutane, 1,2-epoxyoctane, 1,2-epoxyhexane, 1,2-epoxydecane,1,2-epoxytetradecane, 1,2-epoxyhexadecane, 1,2-epoxyoctadecane,1,2-epoxyeicosane, 1,2-epoxycyclopentane, 1,2-epoxycyclohexane and1,2-epoxycyclododecane. These alkylene oxides may be used as acombination of two or more thereof. Of these, ethylene oxide andpropylene oxide are preferable because of ease in availability.

The unsaturated epoxide includes, example, diene monoepoxides, glycidylether of α,β-ethylenically unsaturated compounds, and glycidyl ester ofcarboxyl group-containing α,β-ethylenically unsaturated compounds.

As specific examples of the diene monoepoxide, there can be mentionedbutadiene monoepoxide, chloroprene monoepoxide, 4,5-epoxy-2-pentene,epoxy-1-vinylcyclohexene and 1,2-epoxy-5,9-cyclododecadiene.

As specific examples of the glycidyl other of an α,β-ethylenicallyunsaturated compound, there can be mentioned vinyl glycidyl ether, allylglycidyl ether, vinylcyclohexane glycidyl ether and o-allylphenylglycidyl ether.

As specific examples of the glycidyl ester of a carboxylgroup-containing α,β-ethylenically unsaturated compound, there can bementioned glycidyl acrylate, glycidyl methacrylate, glycidyl crotonate,glycidyl 4-heptenate, glycidyl solbate, glycidyl linolate, glycidylester of 3-cyclohexenecarboxylic acid and glycidyl ester of4-methyl-3-cyclohexenecarboxylic acid.

These unsaturated epoxides may be used as a combination of two or morethereof. Of these, allyl glycidyl ether and glycidyl methacrylate arepreferable because of ease in availability.

The Mooney viscosity (ML₁₊₄, 100° C.) of epihalohydrin rubber (B) is notparticularly limited, but, its lower limit is preferably 30 and morepreferably 40, and its upper limit is preferably 140 and more preferably90. When the Mooney viscosity is too high or too low, the processabilityof rubber is degraded.

The ratio in amount of nitrile rubber (A) and epihalohydrin rubber (B)in the rubber composition for a hose of the present invention is suchthat the lower limit of the ratio of nitrile rubber (A) to the sum ofnitrile rubber (A) and epihalohydrin rubber (B) is 25% by weight,preferably 35% by weight and more preferably 45% by weight, and theupper limit thereof is 80% by weight, preferably 75% by weight and morepreferably 70% by weight. That is, the lower limit of the ratio ofepihalohydrin rubber (B) to the sum of nitrile rubber (A) andepihalohydrin rubber (B) is 20% by weight, preferably 25% by weight andmore preferably 30% by weight, and the upper limit thereof is 75% byweight, preferably 65% by weight and more preferably 55% by weight. Ifthe amount of nitrile rubber (A) is too small and the amount ofepihalohydrin rubber (B) is too large, the resistance to fuel oilresistance is reduced. In contrast, if the amount of nitrile rubber (A)is too large and the amount of epihalohydrin rubber (B) is too small,the cold resistance is reduced.

Crosslinking Agent

The rubber composition for a hose of the present invention comprises asan indispensable ingredient a crosslinking agent (C_(A)) for nitrilerubber (A) and/or a crosslinking agent (C_(B)) for epihalohydrin rubber(B). Of the two crosslinking agents, crosslinking agent (C_(A)) fornitrile rubber (A) is preferable in view of the high mechanicalstrength. More preferably both of crosslinking agent (C_(A)) for nitrilerubber (A) and crosslinking agent (C_(B)) for epihalohydrin rubber (B)are contained.

The amount of the crosslinking agent is preferably in the range of 0.1phr to 8 phr based on the sum in weight of nitrile rubber (A) andepihalohydrin rubber (B). By the term “phr” as used herein we mean theamount expressed by parts by weight per 100 parts by weight of rubber,i.e., per 100 parts by weight of the sum of nitrile rubber (A) andepihalohydrin rubber (B). This term is also used for the amounts ofother ingredients hereinafter explained.

Crosslinking Agent (C_(A)) for Nitrile Rubber (A)

The crosslinking agent (C_(A)) for nitrile rubber includes, for example,sulfur-containing crosslinking agents and organic peroxide crosslinkingagents. Of these, sulfur-containing crosslinking agents are preferablebecause of good storage stability and molding properties of the rubbercomposition.

The sulfur-containing crosslinking agent is not particularly limited,and includes sulfur and sulfur-donor compounds. As specific examples ofthe sulfur-donor compound, there can be mentioned tetramethylthiuramdisulfide, tetraethylthiuram disulfide, dipentamethylenethiuramdisulfide, morpholine disulfide and alkylphenol disulfide. Of thesulfur-containing crosslinking agents, sulfur is preferable. The amountof the sulfur-containing crosslinking agent is such that the lower limitis 0.1 phr and preferably 0.3 phr and the upper limit is 10 phr,preferably 8 phr and more preferably 7 phr.

A crosslinking accelerator and accelerator activator can be used incombination with the sulfur-containing crosslinking agent.

As the crosslinking accelerator, those which are conventionally used fornitrile rubber are mentioned. The crosslinking accelerator preferablyincludes thiuram accelerators, thiazole accelerators and sulfenamideaccelerators. As specific examples of the thiuram accelerator, there canbe mentioned tetramethylthiuram monosulfide, tetramethylthiuramdisulfide, tetramethylthiuram monosulfide and tetraethylthiuramdisulfide. As specific examples of the thiazole accelerator, there canbe mentioned 2-mercaptobenzothiazole and dibenzothiazyl disulfide. Asspecific examples of the sulfenamide accelerator, there can be mentionedN-cyclohexyl-2-benzothiazylsulfenamide andN-oxydiethylene-2-benzothiazylsulfenamide. These crosslinkingaccelerators may be used as a combination of at least two thereof. Theamount of the crosslinking accelerator is preferably not larger than 12phr and more preferably not larger than 10 phr.

The accelerator activator is not particularly limited, and include, forexample, fatty acids, fatty acid metal salts and metal oxides. Asspecific examples of the fatty acid, there can be mentioned stearicacid, oleic acid and lauric acid. As specific examples of the fatty acidmetal salts, there can be mentioned zinc salts of the above-recitedfatty acids. The amounts of fatty acid and fatty acid zinc salt arepreferably not larger than 5 phr and more preferably not larger than 3phr. As specific examples of the metal oxides, there can be mentionedzinc oxide and magnesium oxide. The amount of metal oxide is preferablynot larger than 15 phr and more preferably not larger than 10 phr.

The organic peroxide crosslinking agent is not particularly limited,and, as specific examples thereof, there can be mentioned dicumylperoxide, di-t-butyl peroxide, t-butylcumyl peroxide, benzoyl peroxide,2,4-dichlorobenzoyl peroxide,2,5-dimethyl-2,5-di(t-butylperoxy)-hexyne-3,1,1-di-(t-butylperoxy)-3,3,5-trimethylcyclohexane,1,3-di(t-butylperoxyisopropyl)benzene,2,5-dimethyl-2,5-di(benzoylperoxy)hexane and t-butylperoxy benzoate.These organic peroxide crosslinking agents may be used as a combinationof at least two thereof. The amount of organic peroxide crosslinkingagent is such that the lower limit is 0.1 phr and preferably 0.2 phr,and the upper limit is 10 phr, preferably 8 phr and more preferably 5phr.

In combination with the organic peroxide crosslinking agent, a compoundhaving at least two cross-linking unsaturated bonds in the molecule canbe used as a crosslinking activator. As specific examples of thecrosslinking activator, there can be mentioned ethylene dimethacrylate,diallyl phthalate, N,N-m-phenylene dimaleimide, divinylbenzene, triallylisocyanurate, trimethylolpropane trimethacryalte and liquid vinylpolybutadiene. These crosslinking activators may be used as acombination of at least two thereof. The amount of crosslinkingactivator is preferably not larger than 10 ppm and more preferably notlarger than 5 ppm.

Crosslinking Agent (C_(B)) for Epihalohydrin Rubber (A)

The crosslinking agent (C_(B)) for epihalohydrin rubber includes, forexample, thioureas, triazines, quinoxalines and amines. Of these,thioureas and triazines are preferable in view of the crosslinkingproperty. As specific examples of the thioureas, there can be mentionedethylene thiourea, diethylthiourea, dibutylthiourea, dilaurylthiourea,trimethylthiourea and diphenylthiourea. Of these, ethylene thiourea ispreferable. The triazines used are triazine compounds having at leasttwo mercapto groups, which may have a substituent such as, for example,alkyl group, alkyamino group or dialkylamino group, each alkyl grouphaving 1 to 10 carbon atoms. As specific examples of the triazines,there can be mentioned 2,4,6-trimercapto-s-triazine,2-methyl-4,6-dimercapto-s-triazine,2-ethylamino-4,6-dimercapto-s-trazine and2-diethylamino-4,6-dimercapto-s-triazine. Of these,2,4,6-trimercapto-s-triazine is preferable. The quinoxalines include2,3-dimercaptoquinoxaline compounds and quinoxaline-2,3-dithiocarbonatecompounds. These compounds may have an alkyl substituent with 1 to 4carbon atoms. As specific examples of the quinoxalines, there can bementioned 2,3-dimercaptoquinoxaline, quinoxaline-2,3-dithiocarbonate,6-methylquinoxaline-2,3-dithiocarbonate,6-isopropylquinoxaline-2,3-dithiocarbonate and5,8-dimethylquinoxaline-2,3-dithiocarbonate. The amines includepolyamine compounds having 2 to 20 carbon atoms. As specific examples ofthe amines, there can be mentioned hexamethylene diamine, triethylenetetramine, tetraethylene pentamine,N,N′-dicinnamylidene-1,6-hexanediamine, hexamethylene diamine carbamateand 4,4′-methylenebis(cyclohexylamine)carbamate. The amount of thecrosslinking agent (C_(B)) for epihalohydrin rubber is such that thelower limit is 0.1 phr and preferably 0.2 phr, and the upper limit is 8phr and preferably 5 phr.

An acid acceptor and a crosslinking accelerator can be used incombination with the crosslinking agent (C_(B)) for epihalohydrinrubber.

The acid acceptor includes, for example, oxides, hydroxides, carbonates,carboxylates, silicates, borates, metaborates and phosphites of metalsof group II of the periodic table; oxides, basic carbonates, basiccarboxylates, basic phosphites, basic sulfites and tribasic sulfates ofmetals of group IVA of the periodic table; and hydrotalcites representedby the general formula: Mg_(x)Al_(y)(OH)_(2X+3Y−2)CO₃·wH₂O wherein X isa number of 1 to 10, Y is a number of 1 to 5, and w is a real number. Asspecific examples of the acid acceptor, there can be mentioned magnesiumoxide, magnesium hydroxide, barium hydroxide, magnesium carbonate,barium carbonate, calcium oxide (quicklime), calcium hydroxide (slakedlime), calcium carbonate, calcium silicate, magnesium metaborate,calcium metaborate, barium metaborate, calcium stearate, zinc stearate,tin stearate, calcium phthalate, calcium phosphite, zinc oxide, tinoxide, basic tin phosphite, Mg_(4.5)Al₂(OH)₁₃CO₃·3.5H₂O,Mg_(4.5)Al₂(OH)₁₃CO₃ and Mg₆Al₂(OH)₁₆CO₃·4H₂O. The amount of the acidacceptor is preferably not larger than 20 phr and more preferably 15phr.

The crosslinking accelerator includes, for example, organic bases havinga dissociation constant pKa of at least 7, salts of organic basescapable of producing bases having a dissociation constant pKa of atleast 7, and organic acid salts having a dissociation constant pKa of atleast 7(see Dai Yuki Kagaku, compiled under the supervision of MujioKotake, annex vol. 2 [manual of Constants in Organic Chemistry],p585-613, published by Asakura Shoten). As examples of the organicbases, there can be mentioned aliphatic amines and aromatic amines,which have 1 to 20 carbon atoms, guanidines having a substituent such asan alkyl or aryl group having 1 to 10 carbon atoms, andnitrogen-containing cyclic compounds having 3 to 20 carbon atoms.

As specific examples of the organic gases, there can be mentionedbenzylamine, dibenzylamine, guanidine, diphenylguanidine,diorthotolylguanidine, piperidine, pyrrolidine,1,8-diaza-bicyclo(5,4,0)undecene-7 (DBU) and N-methylmorpholine. Theorganic gases are not limited thereto. Of these, diphenylguanidine and1,8-diaza-bicyclo(5,4,0)undecene-7 are preferable.

As examples of the salts of organic bases, there can be mentionedcarbonate salts, phenol salts, hydrochloride salts, sulfate salts andoxalate salts of the above-recited organic bases. As examples of theorganic acid salts, there can be mentioned sodium salts, potassiumsalts, zinc salts and piperidine salts of dithiocarbamic acids. Thedithiocarbamic acids include dithiocarbamic acid compounds having asubstituent such as an alkyl or aryl group having 1 to 10 carbon atoms.As specific examples of the dithiocarbamic acid compounds, there can bementioned dimethyldithiocarbamic acid, diethyldithiocarbamic acid,dibutyldithiocarbamic acid, ethylphenyldithiocarbamic acid anddibenzyldithiocarbamic acid. The amount of the crosslinking acceleratoris preferably not larger than 8 phr and more preferably 5 phr.

Other Ingredients

The rubber composition of the present invention can contain otheringredients such as a reinforcer, a filler, a plasticizer, anantioxidant, a crosslinking retarder and a processing aid.

The reinforcer includes, for example, carbon black and silica.

The filler includes, for example, calcium carbonate, clay and talc.

The plasticizer includes, for example, di(butoxy-ethoxyethyl) adipate,di(2-ethylhexyl) adipate and di-(2-ethylhexyl) phthalate.

The antioxidant includes, for example, 2-mercaptobenzimidazole, apolymerized product of 2,2,4-triethyl-1,2-dihydroquinoline and nickeldibutyldithiocarbamic acid.

The crosslinking retarder includes, for example,N-cyclohexylthiophthalimide, phthalic anhydride and acetylsalicylicacid.

The processing aid includes, for example, fatty acids such as stearicacid and hydroxystearic acid, and salts of these fatty acids, fatty acidesters such as sorbitan stearate and n-butyl stearate, and fatty acidamides such as stearamide, oleylamide and laurilamide.

The amount of those ingredients is appropriately chosen depending uponthe processing conditions and properties required for the crosslinkedrubber product.

The method of preparing the rubber composition for a hose of the presentinvention is not particularly limited. For example, the rubbercomposition is prepared by a method of mixing together nitrile rubber(A), epihalohydrin rubber (B), crosslinking agent (C_(A)) for nitrilerubber (A) and/or crosslinking agent (C_(B)) for epihalohydrin rubber(B), and other ingredients by using a kneader such as an open roll,Banbury mixer or an internal mixer. The order of mixing the respectiveingredients is not particularly limited. For example, first, nitrilerubber (A) and epihalohydrin rubber (B) are mixed together, and then theother ingredients are mixed with the rubber mixture; or, each of nitrilerubber (A) and epihalohydrin rubber (B) is mixed together with otheringredients, and the two rubber mixtures are mixed together.

The rubber composition for a hose of the present invention preferablyexhibits an adequate rubber hardness when it is crosslinked. Thehardness of a crosslinked rubber is such that the lower limit of the JISA hardness is preferably 40°, more preferably 50° and especiallypreferably 60°, and the upper limit thereof is preferably 95°, morepreferably 90° and especially preferably 85°. When the hardness of acrosslinked rubber is too low, problems sometimes to arise in that theconnection failure is caused between a hose and a fitting, and a hose isbent leading to prevention of flow of fluid stream. In contrast, whenthe hardness of a crosslinked rubber is too high, the hose becomes toorigid, and handling and fitting properties occasionally becomes poor.The hardness of rubber can be adjusted by appropriately choosing thekinds and amounts of a crosslinking agent, a crosslinking accelerator, areinforcer, a filler and a plasticizer.

Hose

The hose of the present invention has a layer comprised of a crosslinkedproduct of the rubber composition for a hose of the present invention.That is, the hose of the present invention has either a single layerstructure comprised of a crosslinked product of the rubber compositionof the present invention, or a multi-layer structure comprising at leastone layer comprised of a crosslinked product of the rubber compositionof the present invention.

The crosslinking of the rubber composition of the present invention forthe production of a hose is carried out after the rubber composition isshaped into a form of hose.

The shaping of the rubber composition of the present invention into ahose form can be carried out by various methods and an adequate methodcan be chosen depending upon the structure and shape of hose. Theshaping method is not particularly limited and includes, for example, anextrusion method using a single screw extruder or a multi-screwextruder, and a molding method using an injection molding machine, atransfer molding machine or a press molding machine. The shapingconditions employed are appropriately chosen in consideration ofproductivity, viscosity of the rubber composition and the extent ofprogress of crosslinking reaction. Thus shaping temperature and shapingtime are appropriately chosen so that the shapability is notdeteriorated.

As for the crosslinking conditions, adequate crosslinking temperatureand crosslinking time are chosen depending upon the particularcharacteristics of the rubber composition. Usually the crosslinkingtemperature is in the range of 80° C. to 250° C., preferably 100° C. to230° C., and the crosslinking time is in the range of 20 seconds to 30hours, preferably 1 minute to 24 hours. According to the need, asecondary crosslinking can be carried out.

The method of heating for crosslinking the rubber composition includes,for example, a high-pressure high-temperature steam heating method, ahigh-temperature air heating method, a high-temperature co-molten saltheating method, a high-frequency heating method, and a method of placingthe rubber composition within a mold heated by electrical heating.Usually the rubber composition of a hose shape is heated within ahigh-pressure can by using high-pressure and high-temperature steam. Therubber composition of a hose shape is usually prepared by an extrusionmethod, but, the method of shaping is not particularly limited and othermethods can be employed.

To satisfy various properties required for a hose, the hose of thepresent invention may have a layer comprised of a crosslinked product ofother rubber composition or a layer comprised of an oil-resistant resin.

The rubber composition used for forming the layer contained incombination with the layer formed from the rubber composition of thepresent invention, includes, for example, a nitrile rubber, ahydrogenated nitrile, an epihalohydrin rubber, a chloroprene rubber,chlorosulfonated polyethylene, chlorinated polyethylene, an acrylicrubber and a fluororubber. The rubber compositions comprising theserubbers are prepared by incorporating a crosslinking agent and acrosslinking activator, which are adequate for the respective rubbers,in the rubbers.

As specific examples of the oil-resistant resin, there can be mentioneda fluoro-resin, a fluorine-containing thermoplastic elastomer, a nylonresin, a thermoplastic polyamide elastomer, a polyester resin, athermoplastic polyester elastomer and a thermoplastic polyurethaneelastomer.

The hose of the present invention may have a reinforcing layer comprisedof, for example, a natural fiber, a chemical fiber or a metal wire. Asspecific examples of the natural fiber, there can be mentioned cottonand linen. As specific examples of the chemical fiber, there can bementioned rayon, vinylon, nylon, polyester fiber and polypropylenefiber. As specific examples of the metal wire, there can be mentioned astainless steel wire and a steel wire.

When the hose of the present invention has a multi-layer structure withadjacent layers comprised of different kinds of ingredients, a specialadhesive can be applied between the adjacent layers or anadhesion-enhancing aid can be incorporated in the rubber composition, toimprove the inter-layer bonding force.

For making a hose having a multi-layer structure, the same hose-shapingmethod can be repeated plural times or a plurality kinds of shapingmethods can be combined. For example, there can be employed a methodwherein an innermost rubber composition layer of a hose is formed on theperipheral of a mandrel by using a first extruder, a reinforcing layercomprised of a polyester layer is formed on the peripheral of theinnermost rubber composition layer, and then an outermost rubbercomposition layer is formed on the peripheral of the reinforcing layerby using a second extruder.

The hose of the present invention has a crosslinked rubber layer formedfrom the rubber composition of the present invention and exhibiting wellbalanced resistance to fuel permeation and cold resistance. Therefore,the hose of the present invention prevents or minimized a liquid fuelsuch as gasoline, kerosine and gas oil, and gaseous fuel to permeatethrough the hose wall and to be dissipated into the air, and the hoseexhibits good cold resistance.

The hose of the present invention can be used, for example, as a fueloil hose, a fuel gas hose, a lubricating oil hose and an air hose.Especially the hose is suitable for use, in which the desired hosecharacteristics are required at a low temperature below −30° C., such asautomobile parts.

As specific examples of the hose used as automobile parts, there can bementioned hoses used in a fuel system, a brake system, a power-steeringsystem, a control system, an air-conditioning system, an air suctionsystem, an oil-cooling system, a clutch system and a suspension system.More specifically, the fuel system includes, for example, a fuel hoseand a fuel inlet hose. The brake system includes, for example, ahydraulic brake hose and a vacuum brake hose. The power steering systemincludes, for example, a high-pressure power steering hose and a suctionhose. The control system includes, for example, a ventilation hose and avacuum-sensing hose. Of these hoses, the hose of the present inventionis especially suitable for a fuel hose and a fuel inlet hose, for whicha high resistance to fuel permeation is required.

The invention will now be specifically described by the followingexamples and comparative examples. In these, working examples, parts andpercents are by weight.

EXAMPLE 1

(Preparation of Rubber Composition)

Using a Banbury mixer, 50 parts of nitrile rubber A1, 50 parts ofepihalohydrin rubber B1, 30 parts of carbon black (#60 available fromAsahi Carbon Co., Ltd.), 1.0 part of stearic acid. 10 parts of aplasticizer (“Thiokol TP-95”™ available from Morton International Ltd.),5 parts of zinc oxide (zinc flower #1 available from Sakai Chem. Ind.Co., Ltd.) and 1.5 parts of an acid acceptor (magnesium oxide, “KyowaMag 150”™ available from Kyowa Chem. Ind. Co., Ltd.) were kneadedtogether. The kneaded mixture was mixed with 1.0 part of crosslinkingagent C_(A)1 for nitrile rubber (sulfur), 1.0 part of a crosslinkingaccelerator (“Nocceler DM”™ available from Ouchi Shinko ChemicalIndustrial Co., Ltd.) and 2.0 parts of crosslinking agent C_(B)1 forepihalohydrin rubber (ethylene thiourea, “Accel 22”™, available fromKawaguchi Chem. Ind. Co., Ltd. ) by using an open roll to prepare arubber composition.

(Preparation of Crosslinked Rubber Sheet and Tensile Tests)

The obtained rubber composition was crosslinked at 160° C. for 15minutes by using a steam platen press to prepare a crosslinked rubbersheet having a thickness of 2 mm. Tensile strength, breaking elongationand hardness of the crosslinked rubber sheet were measured according toJIS K630. The results are shown in Table 1.

(Test of Resistance to Fuel Oil Permeation of Crosslinked Rubber Sheet)

Resistance of fuel oil permeation of the crosslinked rubber sheet wasmeasured as follows. 50 ml of a test fuel oil C (mixture ofisooctane/toluene [50/50 by volume]) was placed in 100 ml tare volumealuminum cup, and a crosslinked rubber sheet cut into a circular shapehaving a diameter of 61 mm was tented on the open-end edge of the cup bya clamp. The cup was kept the bottom up at 23° C. within a thermostat.The whole weight of the cup was measured at every 24 hours to determinethe reduction in weight of fuel oil per hour. The measurement wasrepeated until the weight reduction became constant. The amount of fueloil permeated through the crosslinked rubber sheet per day wascalculated from the contact area of the crosslinked rubber sheet withthe fuel oil, and the thickness of the crosslinked rubber sheet. Thefuel oil permeation as measured on the crosslinked rubber sheet is shownin Table 1. The smaller the measured value for fuel oil permeation, themore excellent the crosslinked rubber sheet in resistance to fuel oilpermeation.

(Test for Cold Resistance of Crosslinked Rubber Sheet)

Cold resistance of the crosslinked rubber sheet was measured by alow-temperature impact brittleness testing method according to JISK6301. The low-temperature impact brittle point is shown in Table 1. Thelower the low-temperature impact brittle point, the more excellent thecrosslinked rubber sheet in cold resistance.

(Production of Hose)

The rubber composition was extruded into a tube having an inner diameterof 10 mm and a wall thickness of 2.0 mm by using a single-screwextruder. A metal mandrel having an outer diameter of 10 mm was insertedinto the rubber tube. The rubber tube/metal mandrel composite was placedin a pressure-resistant can, and then heated at 160° C. for 45 minutesby high-pressure steam heating to be thereby crosslinked. Thereafter themandrel was drawn from the rubber tube to make a cylindrical hose havinga single layer structure.

(Test of Resistance to Fuel Oil Permeation of Hose)

Resistance of fuel oil permeation of the hose was measured as follows.The hose was cut to a length of 200 mm. A metal rod having a diameter of10 mm and a length of 20 mm was inserted into one end of the cut hose,and the metal rod-inserted end portion was sealed with a teflon tape. 12ml of fuel oil C was introduced into the hose through the open endthereof, and then this end portion was sealed in the same manner as themetal rod-inserted end portion. Then the hose was left to stand at 23°C. for 48 hours within a thermostat. The fuel oil permeation wascalculated from the weight of the oil-introduced hose as measured beforeand after the standing at 23° C. for 48 hours. The fuel oil permeationas measured on the hose is shown in Table 1. The smaller the measuredvalue for fuel oil permeation, the more excellent the hose in resistanceto fuel oil permeation.

(Test for Cold Resistance of Hose)

Cold resistance of the hose was measured as follows. The hose cut into alength of 200 mm was left to stand for 2 hours within a thermostatmaintained at a predetermined temperature. Flexural test was conductedat a folding angle of 90° while the hose was maintained at thattemperature. After the test, occurrence of cracks was examined. The testtemperature was −30° C. and −35° C. The test results are shown inTable 1. Rating “A” means that crack occurrence was not observed, andrating “B” means that crack occurrence was observed. When crackoccurrence is not observed at a lower temperature, the hose is excellentin cold resistance.

EXAMPLES 2-4 COMPARATIVE EXAMPLES 1-3

The tests were conducted in the same manner as in Examples 1 except thatthe rubber compositions shown in Tables 1 and 2 were used with all otherconditions remaining the same. The results obtained in Examples 2-4 areshown in Table 1, and the results obtained in Comparative Examples 1-3are shown in Table 2.

TABLE 1 Examples Example No. 1 2 3 4 Composition (parts) Nitrile rubberA1*¹ 50 — — 40 Acrylonitrile unit content: 53% Nitrile rubber A2*² — 6070 — Acrylonitrile unit content: 50% Nitrile rubber A3*³ — — — —Acrylonitrile unit content: 42.5% Epihalohydrin rubber B1*⁴ 50 — 30 —Epihalohydrin rubber B2*⁵ — 40 — 60 Crosslinking agent C_(A)1 1 1 1.5 1for nitrile rubber: sulfur Crosslinking accelerator*⁶ 1 1 1.5 1 Acidacceptor: magnesium oxide*⁷ 1.5 1.5 — 1.5 Crosslinking agent C_(B)1 2 2— — for epihalohydrin rubber*⁸ Crosslinking agent C_(B)2 — — — 0.5 forepihalohydrin rubber*⁹ Properties of crosslinked rubber sheet Permeationof fuel oil C 195 205 214 225 (g · mm/m² · day) Low-temp. impact brittlepoint −28 −27 −27 −32 (° C.) Tensile strength (MPa) 15.2 15.6 15.7 14.8Breaking elongation (%) 290 310 350 330 Hardness (JIS A) 69 71 70 71Properties of hose Permeation of fuel oil C (g/day) 0.25 0.29 0.32 0.34Cold resistance at −30° C. A A A A at −35° C. A A A A

TABLE 2 Comparative Examples Example No. 1 2 3 Composition (parts)Nitrile rubber A1*¹ — 90 10 Acrylonitrile unit content: 53% Nitrilerubber A2*² — — — Acrylonitrile unit content: 50% Nitrile rubber A3*³ 50— — Acrylonitrile unit content: 42.5% Epihalohydrin rubber B1*⁴ 50 — 90Epihalohydrin rubber B2*⁵ — — — Crosslinking agent C_(A)1 1 1 1 fornitrile rubber: sulfur Crosslinking accelerator*⁶ 1 1 1 Acid acceptor:magnesium oxide*⁷ 1.5 1.5 1.5 Crosslinking agent C_(B)1 2 2 2 forepihalohydrin rubber*⁸ Crosslinking agent C_(B)2 — — — for epihalohydrinrubber*⁹ Properties of crosslinked rubber sheet Permeation of fuel oil C365 190 345 (g · mm/m² · day) Low-temp. impact brittle point −32 −18 −34(° C.) Tensile strength (MPa) 14.4 17.5 14.3 Breaking elongation (%) 320340 530 Hardness (JIS A) 68 72 69 Properties of hose Permeation of fueloil C (g/day) 0.64 0.23 0.59 Cold resistance at −30° C. A B A at −35° C.A B A *¹“Nipol DN002” ™ available from Nippon Zeon Co., acrylonitrilecontent: 53%, ML₁₊₄,100° C.: 50 *²“Nipol DN003” ™ available from NipponZeon Co., acrylonitrile content: 50%, ML₁₊₄,100° C.: 78 *³“NipolDN101L” ™ available from Nippon Zeon Co., acrylonitrile content: 42.5%,ML₁₊₄,100° C.: 60 *⁴“Gechron 3100” ™ available from Nippon Zeon Co.,epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer, ML₁₊₄,100° C.: 70 *⁵“Gechron 1100” ™ available from Nippon Zeon Co.,epichlorohydrin-allyl glycidyl ether copolymer, ML₁₊₄,100° C.: 58*⁶“Nocceler DM” ™ available from Ouchi Shinko Chemical Industrial Co.,Ltd., dibenzothiazyl disulfide *⁷“Kyowa Mag 150” ™ available from KyowaChem. Ind. Co., Ltd., magnesium oxide *⁸“Accel 22” ™ available fromKawaguchi Chem. Ind. Co., Ltd., ethylene thiourea*⁹2,4,6-trimercapto-s-triazine, supplied by Sankyo Kasei Co., Ltd.

The rubber composition used in Comparative Example 1 contained a nitrilerubber A3 having an acrylonitrile content smaller than that of a nitrilerubber used in the present invention. Therefore, the crosslinked rubberof Comparative Example 1 is greatly inferior in resistance to fuel oilpermeation as compared with the crosslinked rubber of Example 1.

The rubber composition used in Comparative Example 2 contained a nitrilerubber in an amount larger than that in the rubber composition of thepresent invention. Therefore, the crosslinked rubber of ComparativeExample 2 is greatly inferior in cold resistance as compared with thecrosslinked rubber of Example 1.

The rubber composition used in Comparative Example 3 contained a nitrilerubber in an amount smaller than that in the rubber composition of thepresent invention. Therefore, the crosslinked rubber of ComparativeExample 3 is greatly inferior in resistance to fuel oil permeation ascompared with the crosslinked rubber of Example 1.

In contrast, the rubber compositions in Examples 1 to 4 and hoses havinga layer comprised of each of the rubber compositions have well balancedresistance to fuel oil resistance and cold resistance.

INDUSTRIAL APPLICABILITY

In accordance with the present invention, there are provided a rubbercomposition capable of forming a hose having excellent resistance tofuel oil resistance and cold resistance, and further provided a hosehaving a layer comprised of said rubber composition. The hose of thepresent invention is especially suitable for a fuel oil hose of anautomobile.

What is claimed is:
 1. A rubber composition for a hose, which comprisesa nitrile rubber (A) comprising 45 to 55% by weight of α,β-ethylenicallyunsaturated nitrile monomer units and 55 to 45% by weight of conjugateddiene monomer units, an epihalohydrin rubber (B), and a crosslinkingagent (C_(A)) for the nitrile rubber (A) and a crosslinking agent(C_(B)) for the epihalohydrin rubber (B); the amount of the nitrilerubber (A) being in the range of 45 to 70% by weight based on the sum ofthe nitrile rubber (A) and the epihalohydrin rubber (B).
 2. The rubbercomposition according to claim 1, wherein the total amount of thecrosslinking agent (C_(A)) for the nitrile rubber (A) and thecrosslinking agent (C_(B)) for the epihalohydrin rubber (B) is in therange of 0.1 to 8 parts by weight based on 100 parts by weight of thesum of the nitrile rubber (A) and the epihalohydrin rubber (B).
 3. Therubber composition according to claim 1, wherein the nitrile rubber (A)has a Mooney viscosity of 25 to
 100. 4. The rubber composition accordingto claim 1, wherein the α,β-ethylenically unsaturated nitrile monomer isacrylonitrile or methacrylonitrile.
 5. The rubber composition accordingto claim 1, wherein the conjugated diene monomer is 1,3-butadiene,2-methyl-1,3-butadiene, 1,3-pentadiene or 2-chloro-1,3-butadiene.
 6. Therubber composition according to claim 1, wherein the epihalohydrinrubber (B) has a Mooney viscosity of 30 to
 140. 7. The rubbercomposition according to claim 1, wherein the epihalohydrin rubber (B)is a copolymer of an epihalohydrin monomer and an unsaturated epoxidemonomer.
 8. The rubber composition according to claim 7, wherein theepihalohydrin monomer is epichlorohydrin.
 9. The rubber compositionaccording to claim 1, wherein the crosslinking agent (C_(A)) for thenitrite rubber is at least one crosslinking agent selected from thegroup consisting of a sulfur-containing crosslinking agent and anorganic peroxide crosslinking agent.
 10. The rubber compositionaccording to claim 1, wherein the crosslinking agent (C_(B)) for theepihalohydrin rubber is at least one crosslinking agent selected fromthe group consisting of a thiourea, a triazine, a quinoxaline and anamine.
 11. A hose having a layer comprised of a crosslinked product ofthe rubber composition as claimed in any one of claims 1 and 3 to 10.